The invention relates to compositions for use in embolic agents. More specifically, the invention relates to compositions including crosslinkable macromonomers (referred to herein as macromers) that form hydrogels useful in embolization.
Embolic agents are useful for a variety of bioapplications, such as occluding blood vessels, occluding other body lumens such as fallopian tubes, filling aneurysm sacs, as arterial sealants, and as puncture sealants. Embolization of blood vessels is performed for a number of reasons, e.g. to reduce blood flow to and encourage atrophy of tumors, such as in the liver, to reduce blood flow and induce atrophy of uterine fibroids, for treatment of vascular malformations, such as arteriovenous malformations (AVMs) and arteriovenous fistulas (AVFs), to seal endoleaks into aneurysm sacs, to stop uncontrolled bleeding, or to slow bleeding prior to surgery.
Gynecologic embolotherapy may be conducted for a variety of purposes including the treatment of uterine fibroids, the treatment of postpartum and post cesarean bleeding, the treatment of post surgical vaginal bleeding, the prevention and/or treatment of hemorrhage from ectopic pregnancy, prophylactically prior to myomectomy and in obstetrical patients at high risk for bleeding, such as those patients with placenta previa, placenta accreta, uterine fibroids, and twin fetal death.
Abdominal aortic aneurysms (AAA) and thoracic aortic aneurysms (TAA) are relatively rare but often fatal conditions. Open surgery, primarily using clips or ligation techniques, has been the traditional means of treating AAAs and TAAs. Endovascular techniques, i.e. the placement of a stent graft at the site of the aneurysm, have become more popular. The currently available stent graft products, however, are not well matched to the unpredictable and singular anatomy presented by the aneurysm and its surrounding vasculature. Often, there are leaks into the excluded aneurysm sac, termed endoleaks, due to several reasons, including feeder vessels into the sac, spaces between the stent graft and the vessel wall, or holes in the stent graft wall. Such endoleaks can cause the pressure within the aneurysm sac to increase and cause the aneurysm to further expand and to rupture. Various embolic materials, including the devices and materials discussed above, have been placed in the aneurysm sac to induce thrombosis or otherwise to pack the aneurysm sac to seal the endoleak. Embolic materials are also used to occlude feeder vessels into the sac. WO 00/56380 to Micro Therapeutics, Inc. discloses the use of precipitating polymers and prepolymers such as cyanoacrylate to seal endoleaks.
Chemoembolotherapy as used herein refers to the combination of providing mechanical blockage and highly localized, in situ delivery of chemotherapeutic agents. In the treatment of solid tumors, the chemotherapeutic agent acts as an adjunct to the embolization. A known clinical practice is mixing of chemotherapeutic agents with embolic PVA particles for the delivery of the drugs at tumor sites. This type of regional therapy may localize treatment at the site of the tumor, and therefore the therapeutic dose may be smaller than the effective systemic dose, reducing potential side effects and damage to healthy tissue. However, since the chemotherapeutic drug is simply suspended with the beads there is little or no sustained release.
One type of embolic agent that is commonly used for occluding vessels is polyvinyl alcohol (PVA) particles. Such particles are nonspherical and are nonuniform in both size and shape. The particles are delivered via catheter in the vessel upstream of their desired placement site. Upon release, the particles are carried downstream whereupon they eventually lodge in the vessel. The problems associated with presently available PVA embolic particles include recanalization of the vessel, which may require follow up procedures, extensive mixing required to keep the particles suspended during injection, slow injection times and blocking of the catheter due to the high friction coefficient (due to the irregular shape and size of the particles), and inflammation. Other disadvantages of the use of the presently available PVA embolizing particles include lack of control as to where the particles eventually deposit, again due to the size irregularity. Some particles may continue downstream during administration and lodge in the vessel at a point past the desired site of embolization. Some particles may dislodge in the future and drift downstream.
Another issue with the presently available PVA embolic particles is that they are generally made using an aldehyde, such as glutaraldehyde. Such particles must be extracted prior to use, and may contain amounts of the aldehyde in the final product.
BioSphere Medical, Inc. markets microspheres for embolization made from acrylic polymer and impregnated with porcine gelatin. An obvious disadvantage of this product is that it may cause an immune reaction in patients who are sensitive to collagen or gelatin.
Other types of embolic materials that have been used include solid structures such as metallic microcoils, expandable balloons, and expandable materials such as temperature responsive preformed solid polymers and PVA sponges. Microcoils and balloons are limited to use in larger vessels and are prone to recanalization. Extrusion techniques have also been used to deliver extruded polymers to the intended site.
Liquid embolic agents have been developed, which can be delivered to the intended site via a catheter or a syringe, whereupon they solidify to form a solid plug or mass. Temperature responsive polymers have been proposed as embolic agents, as described in WO 00/45868 to University of California. These polymers are in a liquid state when delivered to the intended site and harden in response to the increased temperature of the body.
Another type of liquid embolic agent is compositions containing a polymer in an organic solvent, wherein the polymer precipitates as the solvent is displaced by aqueous based body fluids. See, e.g., U.S. Pat. No. 6,051,607 to Greff and U.S. Pat. No. 5,925,683 to Park. A disadvantage of such products is that the polymer may remain in liquid form for a period of time while the solvent dissipates. The solvent may not completely dissipate from the center of the polymer mass, creating a mass with a solid shell and liquid center. The solvent concentration at the point of injection may increase to a point where small strings of unsolidified polymer material may separate from the polymer mass and be carried away in the blood stream where they can occlude an undesired vascular location. Moreover, the catheter used to deliver the polymer/solvent mixture is typically flushed with solvent before use. This must be done carefully to avoid vascular damage from the solvent.
Another type of liquid embolic agent is monomers that polymerize upon exposure to blood, such as cyanoacrylate. See, e.g. U.S. Pat. No. 6,037,366 to Krall et al. and WO 00/56370 to Micro Therapeutics, Inc. The conventional cyanoacrylate type embolic material is injected into the site of an aneurysm with difficulty because it quickly undergoes curing polymerization in the blood vessel. The material can be very adhesive and a catheter inserted into the blood vessel to deliver the material must be extracted at a stroke as soon as the injection of the material into the site of disease is completed to avoid the catheter being adhered in place. Thus, the material is not easy to handle. The injection cannot be repeated even when the occlusion is imperfect. This embolic material is further disadvantageous in that it can inflict a grave stimulus to the wall of the blood vessel and induce a strong inflammatory reaction.
WO 00/09190 to Incept LLC discloses embolic agents made from two or more liquid polymers that crosslink when combined. The components can be combined in situ at the intended site of embolization.